1. Field of the Invention
The present invention relates to a collimator used to focus a parallel beam on an optical fiber and render parallel to light from the optical fiber.
2. Description of Related Art
Generally, when a high power laser such as a yag laser is used to cut, weld or pierce metals, light from the laser is focused on an optical fiber by a lens and then, transmitted to a place where the metals are machined. A collimator is used to transmit a laser beam to the optical fiber through the lens. The construction of a collimator shown in FIGS. 5 and 6 is disclosed in Japanese Utility Application No. U61-132837, filed on Aug. 29, 1986 by the applicant of the present invention.
Referring now to FIGS. 5 and 6, a collimator comprises a cylindrical receptacle 6 into which a ferrule 4 is fit to receive one end of an optical fiber 2, a cylindrical receptacle holder 8 for holding the receptacle 6, and a cylindrical lens holder 12 for holding a lens 10. A rolling bearing 14 is secured around one end of the receptacle 6. The ferrule 4 is fit into the other end of the receptacle 6. A cap nut 16 is used to prevent the escape of the ferrule 4 from the receptacle 6. A screw 18 limits movement of the cap nut 16.
The receptacle holder 8 includes a receptacle support 8a and a lens holder mount 8b. The receptacle support 8a has a recess 8g to receive the rolling bearing 14 and part of the receptacle 6. The lens holder mount 8b has a light passageway 8h. A step 8c extends radially inwardly from the inner wall of the receptacle holder to provide an optical communication between the recess 8g and the light passageway 8h.
An adjusting mechanism 20 is arranged on the peripheral wall of the receptacle support 8a so as to adjust radial position of the receptacle 6 to align the optical axes of the optical fiber 2 and the lens 10. Four threaded bores 8m extend radially through the receptacle support 8a and are arranged in a circumferentially 90.degree. spaced relationship. Each adjusting mechanism 20 includes a screw 24 received in one of the two diametrically opposite threaded bores 8m, a locking nut 28 on the screw 24, and a spring-loaded screw 26 received in the other threaded bore 8m.
Each screw 24 has a grip 24a at its one end, a pin 24b at the other end, and a thread 24c formed between the grip 24a and the pin 24b. The spring-loaded screw 26 has a spring 26a, an externally threaded member 26b connected to one end of the spring 26a, and a pin 26c connected to the other end of the spring 26a.
Within the recess 8g of the receptacle holder 8, the rolling bearing 14 is supported at four points by the screws 24 and the spring-loaded screws 26. The grip 24a is rotated to cause radial reciprocal movement of the screw 24. As, this occurs, the pin 26c of the spring-loaded screw 26, which is located in a diametrically opposite relation to the grip 24a, is radially moved in a reciprocal fashion under the action of the spring 26a. Thus, the rolling bearing 14 and the receptacle 6 are each moved in two cross directions along a plane extending at right angles to the axis of the receptacle.
An annular retaining plate 30 is secured to the receptacle support 8a by screws 32. A washer 34 and a belleville spring 36 are axially disposed between the retaining plate 30 and the rolling bearing 14. The washer 34 is used to prevent rotation of the outer race of the rolling bearing 14.
The lens holder 12 includes a cylindrical body 12a and a flange 12b. The cylindrical body 12a is threaded into the lens holder mount 8b and secured in position by set screws 38. The lens 10 is fit in the flange 12b and secured by a ring 40 which is, in turn, threaded to the cylindrical body 12a. The flange 12b has through holes 12c to receive bolts.
Again, the ferrule 4 is fixed to the receptacle 6 by the cap nut 16 and supports the optical fiber 2. If the optical fiber 2 is twisted, the receptacle 6 tends to be twisted through the ferrule 4. In such a case, the receptacle 6 is rotated within the receptacle holder 8 through the rolling bearing 14 so as to accommodate a twist of the receptacle. Thus, the optical fiber 2 is not subject to torsional stress.
In order to focus light from a laser, not shown, on the optical fiber 2 by the lens 10, the grip 24a of each adjusting mechanism 20 is rotated to radially move the screw 24 in a reciprocal manner. Then, the rolling bearing 14 and the receptacle 6 are each moved in two cross directions along a vertical plane. This results in optical alignment of the axes of the optical fiber 2 and the lens 10. After this alignment, the locking nut 28 is operated to cause the screw 24 to positively fix the receptacle 6.
Then, the receptacle holder 8 is rotated relative to the lens holder 12 so as to bring the end of the optical fiber 2 into coincident with the focal point of the lens 10. Thereafter, the lens holder 12 is positively fixed to the receptacle holder 8 by means of the set screws 38.
However, the rolling bearing 14 as well as the washer 34 and the belleville spring 36 can not readily be mounted to the collimator although the rolling bearing 14 prevents the optical fiber 2 from being subject to torsional stress. The rolling bearing 14 also complicates the overall structure of the collimator.
In addition, the rolling bearing 14 is axially held in position only by the belleville spring 36 when the grip 24a of each adjusting mechanism 20 is rotated to effect optical alignment. If the weight of the optical fiber 2 is applied to the receptacle 6 through the ferrule 4, then the receptacle 6 is inclined together with the rolling bearing 14 to cause misalignment of the lens 10 and the optical fiber 2. As a result, light passing through the lens 10 cannot properly be focused on the optical fiber 2.